1. Field of the Invention
The present invention relates to a protecting case for covering the outer surface of a magnetic core.
2. Description of the Prior Art
In JP-A No. 115805/1983, there has been proposed a transformer, as is shown in FIG. 1, having a troidal magnetic core 1 being formed of coiled strip material such as a magnetic permeable amorphous metal. The troidal magnetic core made of an amorphous metal becomes very fragile after the quenching thereof, which is necessary to obtain good magnetic properties. If such a fragile magnetic core is submerged in the oil of the transformer as itself, the core is easily chipped, for instance on the edges thereof, due to stresses caused by an external force or due to vibrations of the transformer. If such fragments having been chipped are floated in the oil of the transformer, the properties of the transformer may be lowered or an accident thereof may be caused. In order to avoid such disadvantages, it is necessary to cover the surface of such a troidal core with a cover which is able to prevent floating of chipped fragments.
Conventionally, as is shown in FIG. 2, there is used a core case 2 for protecting a troidal core 1 being comprised of an inner and outer cylindrical members 3A and 3B for covering the inner and outer peripheries of the troidal core 1 respectively, a bottom ring member 4 for covering the lower surface of the core which has an inner and outer upward ribs respectively formed along the inner and outer peripheries thereof, and a cap ring member 5 for covering the upper surface of the core which has an inner and outer downward ribs respectively formed along the inner and outer peripheries thereof. It is necessary to form each of members 3 to 5 of an insulating material such as a synthetic resin so as to have relatively large thickness thereof for containing a heavy magnetic core therein. Further, the inner and outer cylindrical members 3A and 3B are respectively formed to have a gap 6 respectively between the inner periphery of the troidal core and the inner cylindrical member 3A and between the outer periphery of the troidal core and the outer cylindrical member 3B in order to ensure smooth fitting between the troidal core and the inner or outer cylindrical member. After constructing the core case 2 so as to enclose the troidal core therein, a winding 7 is wound around the trunk of the core case and the core case 2 is tightly bound by the winding 7.
However, since the inner and outer cylindrical members 3A and 3B are so formed to have a gap between the magnetic core, there is a possibility that the predetermined magnetic properties of the magnetic core can not be obtained due to deformations of the magnetic core which may be caused by movements thereof upon the construction of the core and/or the winding of the winding 7.
Further, since there are formed two cylindrical space 8 between the core case 2 and the winding 7 wound therearound, the contacting density of the winding 7 to the magnetic core 1 becomes lowered and, due to this, the transformer becomes bulky and uneconomical with the increased length of the conducting wire for forming the winding.
In order to avoid such disadvantages as mentioned above, as is shown in FIG. 2, there considered a method using a tape 9 for wrapping the entire surface of the magnetic core 1 by winding the tape around the core troidally.
However, this method has a disadvantage in that the magnetic energy loss is increased due to possible distortions of the magnetic core which may be caused by stresses exerted thereto upon winding the tape. Moreover, since the taping method is time-consuming and many manufacturing steps are needed, it is improper to the mass production. Regarding to the mentioned above, there considered also a method by insert-molding the magnetic core with a synthetic resin. This method, however, has a disadvantage in that the magnetic energy loss is increased due to distortions of the magnetic core which may be caused by thermal stresses exerted thereto upon the solidification of the resin.